1. Field
This application relates generally to driving circuits, and more specifically to driving circuits for multi-color light emitting diode (LED) systems.
2. Related Art
Multi-color LED systems are becoming widely used for generating arbitrary light colors in various fields of lighting such as architecture. Multi-color LED systems may be used in the future for generating white light for general service lighting, as the ultimate limits on phosphor conversion for “white” LEDs are reached. The most common systems today employ LEDs in three colors: red, green, and blue (RGB); although other systems using different colors or color spectra and/or different numbers of colors are also in use.
In order to generate arbitrary colors or to generate a particular quality of white light, the light output of LEDs of different colors need to be independently controlled. Specifically, the amount of current supplied to each LED or set of LEDs of a particular color needs to be individually controlled, in order that the resultant color is as desired.
Driving circuits for multi-color LED systems to date have been both complicated and large. In applications in which physical space is at a premium, this can be a serious problem. In particular, LED light bulbs have only a tiny space allotted for the power circuitry, as the circuit must fit within the screw base.
The largest components in current state-of-the-art driving circuits for multi-color LED systems are the inductors. The state-of-the-art driving circuits typically include a switcher operating at a relatively low switching frequency and a relatively large current driving the various LEDs. The low switching frequency necessitates a large inductance value, and hence a large physical size, for the inductor, and similarly the large current requirement also results in the need for a large-sized inductor. While it is possible to reduce the size somewhat by switching at a high frequency, such approach may result in electromagnetic interference (EMI) problems; and in any case, with the current state-of-the-art little can be done along these lines to shrink the size of the inductor due to the current requirements.
Finally, current state-of-the-art driving circuits require one inductor for each LED. Thus, in an RGB system, it is necessary to fit three large inductors within the confines of a bulb. Accordingly, it would be desirable to reduce the size of the inductors in a multi-colored LED drive circuit or system, such that the multi-color LED system can fit within the screw base of a LED light bulb and the volume associated therewith, and such that the multi-color LED system may be used in other space-constrained applications.